Field of the Invention
The present invention relates to a winch mechanism for the control of lifting equipment of the type described in the above cross referenced patent, that is to say comprising a rotating drum, the shaft of which is linked to a main drive motor by an electro-magnetic connection system which allows the speed of rotation of the winch to be varied or reversed. My prior U.S. Pat. No. 3,477,695 describes in particular a winch drive mechanism in which the shaft of a winch drum is driven in one direction by a main non-synchronous motor through an eddy current clutch. A smaller auxiliary or overspeed motor is connected to the shaft of the winch drum between the eddy current clutch and the winch drum and is operative to drive the winch drum and in the opposite direction when the clutch is disengaged. When the eddy current clutch is engaged, the overspeed motor is driven in the opposite direction by the main motor. The current of the over speed motor is sensed by an electronic regulator which compares the current signal with a reference signal indicative of a commanded speed and direction of rotation. The electronic regulator generates signal controlling the degree to which the eddy current clutch is energized stabilizing the speed of the winch shaft. In the descent mode, the eddy current clutch is deenergized and the auxiliary or overspeed motor drives the winch shaft in the opposite direction. When an excessive descent speed is sensed, the electronic regulator energizes the eddy current clutch stabilizing the descent rate. This system is suitable for lifting relatively light loads or at relatively low speeds. On the other hand, it is known that the auxiliary motor ensures only the starting operation of the load system during descent. However, it has been established that at the end of a phase of lifting or lowering, the inertia of the load does not immediately immobilize the lifting mechanism when this passes, for example, over a limit security device. In addition, principally for high pressured equipment, the electronic regulator must be connected to electro-magnetic contactors for the power circuits.
Finally, another disadvantage arises from the high cost of the auxiliary motor which, during each operation, must be controlled in the direction of lowering and must process a variable-speed rotor: it is therefore necessary to have a high-slip motor.
The present invention has the aim of remedying these disadvantages and of making an entirely electronic device to control and regulate the direction and speed of rotation of the drum of a lifting winch from a single motor.